Alternating current supply system



April 11, 1944. so 2,346,621

ALTERNATING CURRENT SUPPLY SYSTEM Filed NOV. 13, 1943 2 Sheets-Sheet 1Invent 0r db gepk 60262;

April 11, 1944. J, G, SOLA ALTERNATING CURRENT SUPPLY SYSTEM 2Sheets-Sheet 2 LX112 4x5- IIHH 55 HUN MEG. I

Patented Apr. 11, 1944 ALTEBNATING CURRENT SUPPLY SYSTEM JosephG. Sola,Western Springs, 111., asslgnor to Sola Electric o.I Chicago, 111., acorporation of Delaware Application November 13, 1943, Serial No.510,117

9 Claims.

This invention relates to alternating current supply systems forconsumption circuits having negative resistance characteristics, moreparticularly the invention relates to self-regulating systems forsupplying alternating current at substantially unity power factor toload devices requiring high starting voltages and having resistancecharacteristics which vary inversely with the operating current flowingtherethrough, and the invention has for an object the provision ofimproved, inexpensive and reliable systems of this character. V

While the invention is not limited thereto, it is particularlyapplicable to and will be described in connection with gaseous dischargetubes, such, for example, as cold cathode fluorescent tubes for lightingpurposes. Although cold cathode tubes of the fluorescent type haveheretofore been known, the tendency in the lighting art has been towardthe use of hot cathode tubes due principally to the difllcultiesencountered in supplying cold cathode tubes with the necessary highvoltage for ignition and thereafter controlling the operating currentsupplied thereto.

It has heretofore been proposed to supply such tubes through a highreactance transformer having a sufllciently high secondary voltage toignite or start the current flow in the tube, the transformer being sodesigned that the secondary voltage decreases with increasing currentflow until a stable condition exists. The transformer reactance acts asan inductive ballast in the circuit and thus an undesirable low powerfactor current is drawn from the source of supply. Furthermore it hasbeen found that if the transformer is designed to supply an initialsecondary voltage only high enough to insure breakdown .or starting ofthe tube, the current flow will be stabilized at values considerablyless than the optimum values necessary for the most efllcient operationof the tube, and accordingly the illumination produced by the tube fallsfar short of its maximum capacity.

To increase the initial or open circuit voltage of the transformer'to ahigher value in an attempt to reach a stable condition'wlth the optimumcurrent flowing in the tube results in such a bulky and expensivetransformer structure as to be undesirable, and in addition the higheropen circuit voltage gives'rise to insulation problems which increasesthe expense and may result in danger to the user.

The use of condensers connected in parallel with the tube across thesecondary winding for power factor correction purposes has also beensuggested, but this expedient is ineffective in reducing the size orcost of the transformer and in fact adds to the size and cost of theapparatus because of the size of the condenser necessary to balance theinductance of the transformer. Accordingly, much is yet to be desired insupply systems for load devices of this character having negativeimpedance characteristics, and it is a further object or this inventionto provide a supply system for cold cathode type tubes employed forillumination purposes which is compact, in-

,exmnsive and reliable, which is self-regulating,

and which will supply an optimum operating current to the tube atsubstantially unity power factor.

In my prior Patent No. 2,143,745, issued January 10, 1939, there isdescribed and broadly claimed a constant voltage transformer capable ofgeneral application which employs a high reluctance magnetic shunt foreffecting a relatively loose coupling between the primary and secondarysides in combination with a resonant circuit in the secondary side formaintaining the secondary voltage substantially constant over a widerange of primary voltages. In my later patent, No. 2,212,198, issuedAugust 20, 1940, an additional current-limiting winding and highreluctance shunt are employed, in co-operation with a resonant circuitand shunt similar to that described in my Patent No. 2,143,745, in'orderto provide a limited current supply to a tube or similar load devicehaving a negative resistance characteristic.

In carrying out the present invention, I employ certain of the basicprinciples set forth in my above referred to patents, but the variouselements of my improved systems are differently connected and are soarranged and proportioned as to provide improved, more compact and moreeconomical systems particularly intended for supplying load devices suchas cold cathode fluorescent tubes having negative resistancecharacteristics. Thus I provide, in accordance with one embodiment of myinvention, a transformer having primary and secondary windings adaptedto be respectively connected to an alternating current source ofpredetermined frequency and voltage and to a load such as a cold cathodetube having a negative resistance characteristic. The transformerincludes a high reluctance shunt magnetically disposed between thewindings, which shunt is substantially ineffective when no current flowsin the secondary circuit of the transformer, the shunt functioning uponthe new of current in the secondary winding to divert part of the fluxproduced in the transformer core by the primary and secondary currentsand thus to relax the coupling between the windings. Connected in seriescircuit relation with the secondary winding and the load, I provide acondens er having a capacity reactance so proportioned, relative tocircuit constants of the transformer and the load, as to resonate withthe secondary winding and provide in the secondary load circuit anoscillatory condition of a series resonant nature. The primary andsecondary windings may be electrically separate or may be connectedtogether in auto-transformer relation, as desired, and a plurality ofsecondary windings for supplying separate loads may be associated with asingle primary winding, each secondary winding being serially connectedwith a suitable condenser and load. In the latter case a suitable shuntwill of course be magnetically disposed between each secondary, windingand the common primary winding,

For a more complete understanding of my invention, reference should nowbe had to the drawings in which:

Fig. 1 illustrates a suitable coil and core structure which may beemployed in systems embodying my invention;

Fig. 2 is a somewhat schematic wiring diagram showing one system ofcircuit connections which may be used when the core and coil arrangementof Fig. 1 is employed in carrying out my invention;

Fig. 3 is a somewhat diagrammatic view similar to Fig. 1 but showinganother coil and core arrangement;

Fig. 4 is a circuit diagram of a system embodying my invention andemploying the coil and core arrangement of Fig 3; and

Fig. 5 is a vector diagram showing the phase relations of the voltagewhich may exist in the secondary circuit of a system embodyingmyinvention.

Referring now to Figs. 1 and 2 or the drawings, I have shown myinvention as embodied in a system which comprises a coil and corearrangement or transformer l including a center core I l formed of astack of suitable laminations on the opposite ends of which are mounteda primary winding l2 and a secondary winding l3. In order to providesuitable magnetic return paths for the center core ll, an outer frame isprovided having end legs I 4 and I and upper and lower side legs I6 andH, the end legs l4 and f5 being preferably notched out as shown toreceive the opposite ends of the center core II. The outer frame is ofcourse formed of a suitable stack oflaminations and, as shown, the sidelegs l6 and shown as being of the shel1 type, it will of course beunderstood that other core and coil arrangements may be employed so longas a high reluctance shunt magnetically disposed between the Fig. 2 bythe'reference numeral 25, and the secondary winding 13 is provided withsuitable connecting leads 26 and 21.

In Fig. 2 my improved alternating current supply system is shown asapplied to a negative resistance load which is indicated somewhatdiagrammatically as constituting a cold cathode tube 28 which may be ofthe fluorescent type known in the art and adapted to be employed forlighting purposes. As shown in Fig. 2, one electrode of the tube 28 isconnected to the lead 26 extending from one sheet the secondary windingl3 and the other electrode of the tube 28 is connected by a conductor 29to a condenser 30, the other side of the condenser being connected tothe lead 21 which extends from the other side of the secondary windingl3. Thus the secondary winding l3, the condenser 30 and the tube 28 arecom nected in a closed series circuit.

As will be more fully explained hereinafter, the

- circuit constants of the transformer In, particuval H are providedwith inwardly extending shunt portions which cooperate with oppositelyextend- 7 ing shunt portions on the center core II to provide magneticshunts l3 and I9 between the windings l2 and 13. The shunt portions onthe outer frame terminates short of the corresponding shunt portions onthe core I I so as to leave air gaps 22 of predetermined size in themagnetic shunts.

It will of course be understood that the mag-- netic shunts l8 and I9between the windings may be formed entirely by shunt portions whichextend inwardly from the outer frame legs, or

entirely by shunt portions which extend out-- wardly from the centercore portion H. In either case, however, a small air gap should beprovided in order to provide the desired high reluctance in the shunts.Although the transformer I0 is larly the secondary winding thereof, andthe circuit constants of the-condenser 30 are so proportioned relativeto the circuit constants of the tube 28 as to insure an optimum fiow ofcurrent through the secondary circuit. Preferably, the circuit constantsare so proportioned as to provide an oscillatory condition in the natureof series resonance in the secondary circuit such that the optimum valueof current will flow through the load, the value of the current flowbeing limited by the resonant condition of the secondary circuit and thepermeability of the iron core regardless of the negative resistancecharacteristic of the load. The optimum value of current is maintainedsubstantially constant regardless of-varlations in the voltage appliedto the primary winding i2-from the source 25.

In the embodiment of the invention shown in Figs. 3 and 4, a pair ofsecondary windings 3i and 32 is associated with a single primary winding33. In this embodiment the center core 34 of the transformer 35 isprovided with two sets of outwardly extending shunt portions, and theupper and lower legs 38 and 39 of the outer magnetic frame are providedwith corresponding sets of 1 supply a separate load circuit, areconnected in auto-transformer relation with the primary winding as shownin Fig. 4. Thus the primary winding 33 is connected by means of suitableconductors 42 and 43 to a source of alternating current voltage ofpredetermined frequency indicated by the reference numeral 36. Oneterminal of the secondary winding 32, as shown in Fig. 4, is connectedby a suitable conductor 44 to the conductor 42 leading to one side ofthe primary I winding 33, and the other terminal of the secondarywinding 32 is connected by a conductor 45 to one terminal of a suitableload device or tube 46, the other terminal of the load'device 46 beingconnected by a conductor 41 to a conaacacar denser II, which in turn isconnected to the conductor 42 leading to the other terminal of theprimary winding a. In this manner the primary winding 23 and thesecondary winding 22 are connected in auto-transformer relation inseries circuit with each other and with the load device or tube 40 andthe condenser 48.

Similarly, the secondary winding 2| is connected at one end by aconductor I to the conductor 42 leading to one end of the primarywinding 22, and the other end of the secondary winding Ii is connectedby means of a conductor ii to one terminal of a load device or tube 52,the other terminal of the load device being connected through theconductor 58 to a condenser 54, which in turn is connected by aconductor 55 to the conductor 42 leading to the opposite terminal of theprimary winding 22.

It will of course be understood that the transformer Id of Fig. 1 mayhave its secondary winding connected in auto-transformer relation to theprimary winding, and likewise the transformer 35 of Fig. 3 may have eachor its secondary windings connected to its associated condenser and loadin electrically insulated relation to the primary. In each case,however, the windings must be properly proportioned for the particulartype of connection employed.

In describing the operation of systems embodying my invention, referencewill first be made to the system shown in Figs. 1 and 2. When theprimary winding i2 is first connected to the source of energy 25, amagnetic flux flows through the core II and the return paths provided bythe end and side legs l4, l5, l8, and H of the outer frame so as tothread through the secondary winding is and induce a voltage therein.Since the cold cathode tube 28 is initially nonconducting the secondarycircuit is effectively open circuited and neither the condenser 30 northe magnetic shunts l8 and is will substantially eifect the value of thesecondary voltage. Due to the high reluctance of the air gaps 22 only avery small amount of the primary flux will flow through the shunts andconsequently a secondary voltage substantially equal to the tum-ratiovoltage of the transformer ill will be applied to the tube 28.. Thistum-ratio 'voltage is so chosen as to eiIect breakdown or ignition oftube 28 to render the tube conducting, whereupon a substantial currentimmediately flows between the electrodes of the" tube to produce thedesired illumination.

Immediately upon the now of current in the secondary circuit thecondenser 30 and the magnetic shunts become effective to establish astable self-regulating condition in the secondary circuit whereby anoptimum value of current is established and maintained without regard tothe negative impedance characteristics of the tube and without regard tovariation of the primary voltage over a substantial predetermined range.The capacity reactance of the condenser 30 is preferably so proportionedrelative to the efiective inductance of the secondary winding l3 and theimpedance characteristics of the tube 28 upon the flow of current in thesecondary circuit, as to produce an oscillatory condition in the natureof series resonance in the secondary circuit. Moreover, as soon ascurrent flow begins in the secondary winding II, a back magneto-motiveforce is produced in the section of the core ll surrounded by thesecondary winding which tends to oppose the flow of primary fluxtherethrough, and accordingly a part of the primary flux is directedthrough the shunts II and It so as to reduce or relax the couplingbetween the primary and secondary windings.

It is a known characteristic of series resonant circuits that thecurrent flow therein is limited primarily by the resistance in thecircuit, the inductive reactance and the capacity reactance in thecircuit being substantially equal and opposite. Consequently, thecurrent is substantially in phase with the voltage and substantiallyunity power factor is obtained. In my improved system the magnetic corel0 and the windings l2 and II are so designed as to operatesubstantially at the maximum flux density of the secondary section ofthe core with the optimum value of current flowing through the tube andwith a series res-' onant condition in the secondary circuit. It hasbeen found that following initial breakdown of the tube 28 the secondaryvoltage, instead of dropping as is the case with the usual high leakagereactance transformer employed for igniting such tubes, rises to ahigher value at which a stable condition is reached with optimum currentflow through the tube, which stable condition is determined by theoscillatory condition of the secondary circuit and the maximum fluxdensity condition of the iron core. If the resistance of the tube 28tends to decrease, by reason of its negative characteristic, an increasein current is prevented by the fact that the iron of the secondarycircuit is already at its maximum flux density, and consequently thecurrent flow is maintained at the desired. optimum value regardless ofthe negative resistance characteristic. Operation of the iron at itsmaximum flux density is permissible, since the inductive reactance oithe secondary winding is not utilized as a ballast for absorbing theexcess voltage in order to limit the voltage drop across the tube.

As soon as the oscillatory or series resonant condition is establishedin the secondary circuit, the flux density in the secondary portion ofthe core II rises to a value greater than the flux density in theprimary portion. Accordingly, as the flux density in the primary portionvaries with variations over a wide range in the voltage applied to thewinding i2, the flux density in the secondary core portion will varyonly slightly since more or less flux will be by-passed through themagnetic shunts according to the character of the voltage change on theprimary. Thus the secondary voltage component applied to the tube 28remains substantially constant over a wide range of voltage variation onthe primary wind- 5 ing, insuring constant illumination by the tube.

Fig. 5 is a vector diagram iriustrating a set of voltage conditionswhich may occur, with properly selected circuit constants, in thesecondary circuit of a supply system embodying my invention. Thecurrent, which of course is the same in all parts of the series circuit,may be represented by a vector (not shown) lying along the broken line60 in Fig. 5. The voltage across the secondary winding is accordinglyindicated by the vector IXL, which represents the inductive reactancedrop out of phase with respect to the current, and by the small vectorIRL which represents the resistance drop in phase with the current.Similarly, the voltage across the condenser .is indicated by the vectorIXc 90 out of phase with the current and out of phase with the voltageIXL. The load, which in this case is a cold cathode tube, has inaddition to its pure resistive impedance a substantial capacityreactance, and accordingly the voltage drop across ant secondary voltagerepresented by the vector 12 is slightly out of phase with the current,the current leading the resultant voltage. It will of course beunderstood that a series resonant condition does not require that theinductive and capacitative reactance of the circuit be exactly equal orthat the current and voltage be exactly in phase so as to provide unitypower factor.

The slightly leading current condition shown in Fig. is well within therange of resonant operation and provides a power factor in theneighborhood of unity. If exact resonance and unity power factor aredesired, it is only necessary to correlate the capacity reactances ofthe condenser and tube so that their sum will be equal to the effectiveinductive reactance of the secondary winding with the optimum value ofcurrent flowing in the secondary circuit.

Although my inventionis not limited to any specific dimensions of theiron cores and the windings, or to any specific loads or condensers, butrather contemplates the correlation of the various circuit'constants inaccordance with the voltage and frequency of the source and the currentand voltage rating of the load, the following specifications, which aregiven merely by way of example, may be employed in constructing a systemfor energizing 40 watt cold cathode type fluorescent tubes adapted foroptimum operation with a current flow of approximately 120 milliamperes.A core structure such as is shown in Fig. 3 may be provided having thecenter c0re 34 composed of a stack of laminations approximately 3% inchby inch in cross section, with the outer frame legs 38 and 39 aboutone-half as large in cross section as the center core, the shunts 40,and'll approximately of the same cross section asthe outer frame legs,and the gap in the shunt paths approximately .050- (fifty thou-'sandths) of an inch-in.width.-

On this core. structure may be placed the single primary winding33,.composcdof 1000 turns of The secondary windings are connected inautotransformer relation to the primary winding, as shown in Fig. 4,andthe condensers 48 and 54, connected as shown in Fig. 4, should have acapacitance" or .4 microfarad.

It was found that the transformer, when thus constructed, produced onopen circuit a secondary voltage of approximately' '.600 volts, somewhatless than the'turn-ratio' voltage, with the primary winding connected toa fioflcyclesource of energy 5 at approximately. LIB-volts.

Upon closure'of the primary circuit with the 40 watt tubes connected asshown, it was found that the tubes would be ignited and wouldimmediately operati eat full brilliance with a current No. 26 wire', andthe --two secondary windings 3i and 32 each composed of 4600 turns ofNo. 32 wire.

'tially perfect regulation and constant found to be approximately 90,000lines per square inch.

Tests for temperature rise under short circuit showed a maximumtemperature rise of 26 C. in the primary and 38 C. in the secondaries,and the emciency of the systems was found to be approximately 82%. Whenthe primary voltage was varied between 106 and volts substanlight outputwas observed, the maximum variation being less than 1 It will beapparent from the above description and the illustrative example thatIhave provided a highly efllcient, compact and economical transformer andsupply system for cold cathode tubes, or similar loads having a negativeresist ance characteristic, which is self-regulating and which providesoptimum operation of the load over a wide range of variation in thesupply voltage, and which operates at substantially unity power factor.

A transformer built in accordance with the above specifications, notonly provides more eflicient operation and better regulation than hasheretofore been obtainable, but in addition represents a great saving inmaterials weighing only one-third as much as the high-leakage reactancetransformers heretofore employed for supplying equivalent tubes orloads.

While I have shown particular embodiments of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made,'and I, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. In an alternating current supply system; the combination with analternating current source ofpredetermined voltageand frequency; of agaseous discharge tube having a high initial breakdownvoltage and anegative impedance operating characteristic; a transformer includingmagnetic core means having primary and secondary core portions; saidportions having primary and secondary windings associated therewithrespectively connected across said source and said tube; said windingshaving a turn ratio such that the open'circuit voltage of said secondarywinding is sufficient to effect initial breakdown of said tube; saidcore means including a high reluctance shunt magnetically disposedbetween said windings for relaxing the coupling therebetween upon theflow of current in said secondary winding; said core means'and saidsecondary winding being so proportioned that said secondary core portionoperates at substantially maximum flux density upon the flow of asecondary current corresponding to optimum operation of said tubes; andcapacity reactance means in series circuit relation with said tubeand'said secondary winding; said capacity reactance means, saidsecondary winding and said tube having impedances at said frequency soproportioned as to effect a stable oscillatory condition of operation inthe secondary circuit upon breakdown of said tube thereby to increasethe secondary voltage and cause said optimum current flow through saidtube; said current being limited by said maximum flux density regardlessof said negative impedance characteristic of said tube.

2. In an alternating current supply system, the combination with analternating current source ofpredetermined voltage and frequency of agaseous discharge tube having a high initial breakdown voltage and anegative resistance operating characteristic, a transformer includingprimary and secondary windings disposed on a closed magnetic core andhaving a magnetic shunt disposed between said windings, a condenser, andmeans connecting said condenser in series circuit relation with saidsecondary winding and said tube, said windings having a turn ratio suchthat the open circuit voltage of said secondary winding is sufficient toeffect initial breakdown of said tube and said shunt'being effectiveupon the flow of current in the secondary circuit to vary the degree ofcoupling between said primary and secondary windings, said shunt andsaid secondary winding being so proportioned and arranged relative tosaid condenser and said tube as to establish in said secondary circuit astable oscillatory condition of a series resonant nature when saidprimary winding is energized from said source to produce a current flowin the secondary circuit corresponding to optimum operation of saidtube, the magnetic flux in the secondary section of said corecorresponding substantially to the maximum flux density of the secondarysection of said core upon the flow of said optimum current whereby saidcurrent flow is limited to said optimum regardless of said negativeresistance characteristic of said tube.

3. In an alternating current supply system, the

combination of a gaseous discharge tube having a high initial breakdownvoltage and a negative resistance characteristic, a transformerincluding primary and secondary windings and a magnetic shunt disposedtherebetween, a condenser, and means connecting said condenser in seriescircuit relation with said secondary winding and said tube, saidwindings having a turn ratio such that the open circuit voltage of saidsecondary winding is sufiicient to effect initial breakdown of said tubeand said shunt being effective upon the flowof current in the secondarycircuit to vary the degree of coupling between saidprimary and secondarywindings, the respective impedance characteristics. of said secondarywinding, said produce in said secondary circuit a current flowcorresponding to optimum operation of said tube, said current beinglimited to said optimum value by the maximum flux density of said core,regardless of said negative resistance characteristic of said tube.

5. In an alternating current supply system, the combination with analternating current source of predetermined voltage and frequency, of agaseous discharge tube having a high initial breakdown voltage and anegative impedance operating characteristic, a transformer includingmagnetic core means having primary and secondary portions, said portionshaving primary and secondary windings associated therewith andrespectively connected across said source and said tube and having aturn ratio such that the open circuit voltage of said secondary windingis sumcient to effect initial breakdown of said tube, said transformerincluding a high reluctance shunt magnetically disposed between saidwindings for relaxing the coupling therebetween upon the flow of currentin said secondary winding, said core means and said secondary windingbeing so proportioned that said secondary core portion operates atsubstantially maximum flux density upon the flow of a secondary currentcorresponding to optimum operation of said tube, and capacity reactancemeans connected in series circuit relation with said secondary windingand said tube proportioned to resonate with said secondary winding toproduce said optimum current flow.

6. In an alternating current supply system, the combination with analternating current source of predetermined voltage and frequency, of agaseous discharge tube having a high initial breakdown voltage and anegative impedance operatcondenserand said tube at the frequency ofenergization of said primary winding and the coupling provided by saidshunt beingso proportioned that'a substantially-series resonanteondition is effected in said secondary circuit and said transformer isoperated at substantially its'max irnum flux density in the secondarysection thereoi' whereby a limited but optimum current flows throughsaid tube regardless of the negative resistance characteristic thereof.

4. Inan alternating current supply system, the combination with asubstantially constant frequency alternating current source, of a;gaseous discharge tube having a-highinitial breakdown voltage and anegative resistance operating characteristic, magnetic core meansproviding a'substantially closed magnetic path, primaryand secondarywindings 'on said -core means in magnetically coupled relation,- saidcore means including a high reluctance shunt interposed magneticallybetween said windings whereby the flux threading through one winding maygreatly exceed the flux through the other, and a condenser connected inseries circuit relation with said secondary winding and said tube, saidshunt and said secondary winding being so proportioned and arrangedrelative to said condenser and said tube as to provide in the secondarycircuit an oscillatory operating condition at said frequency in theneighborhood of series resonance thereby to ing characteristic, atransformer including a core having primary and secondary windingsthereon respectively connected across said source and said tubeandhaving a turn ratio such that the open circuit voltage ofsaidsecondary winding is sufficient to effectinitial breakdown of saidtube, said transformer including a high reluctance shunt magneticallydisposed between said windings for relaxing the coupling therebetwe'enupon the flow of current in said secondaryv winding, and ca-' pacityreactance means connected in series circuit relation with said secondarywinding and said tube proportioned to establish upon initial breakdownof said tube an oscillatory condition of a series resonant nature,whereby the operating current flowing in said tube is built up by theresonant constants of the secondary series circuit and is limited by themaximum flux density of said core to an optimum value regardless of thenegative impedance characteristics of said tube.

7 In an alternating current supply system, the combination with analternating current source of predetermined voltage and frequency, of agaseous discharge tube having a high initial breakdown voltage and anegative impedance operating characteristic, a transformer includingprimary and secondary windings respectively connected across said sourceand said tube and having a turn ratio such that the open circuitvoltsaid tube proportioned to establish upon initial breakdown of saidtube an oscillatory condition 01 a series resonant nature, whereby theoperating current flowing in said tube by virtue of the resonantconstants of the secondary series circuit substantially saturates thesecondary section of said core and is limited to an optimum valueregardess of the negative impedance characteristics 01 said tube, saidresonant condition of said secondary circuit being effective to maintainsaid optimum current flow independently of fluctuations in the voltageof said source over a sub, stantial range.

8. In an alternating current supply system, the combination with analternating current source of predetermined voltage and frequency, of agaseous discharge tube having a high initial breakdown voltage and anegative impedance operating characteristic, a transformer includingmagnetic core means having primary and secondary windings disposedthereon and respectively connected across said source-and said tube andhaving a turn ratio such that the open circuit voltage of said secondarywinding is suflicient to effect initial breakdown of said tube, saidcore means including a high reluctance shunt magnetically disposedbetween said windings for relaxing the coupling therebetween upon theflow of current in said secondary winding, said core means and saidsecondary winding being so proportioned that said secondary core portionoperates at substantially maximum flux density upon the flow of asecondary current corresponding to optimum operation of said tube, andcapacity reactance means connected in series circuit relation with saidsecondary winding and said tube, the impedance characteristics of saidsecondary winding, said condenser and said tube at said frequency beingso related as to provide a substantially resonant circuit, whereby saidoptimum but limited current flow through said tube is obtained atsubstantially unity power factor.

9. In an alternating current supply system, the combination with analternating current source oi predetermined voltage and frequency, of agaseous discharge tube having a high initial breakdown voltage and anegative impedance operating characteristic, transformer means includingmagnetizable core means having primary and secondary windings thereon,said windings having a turn ratio such that the open circuit secondaryvoltage is suflicient to eiiect breakdown of said tube when said primarywinding is connected to said source, and a condenser connected in seriescircuit relation with said tube and said secondary winding, saidmagnetizable core means including a high reluctance shunt magneticallydisposed between said windings and effective upon the flow of current insaid secondary winding to relax the coupling between said windings, saidcondenser having an impedance so proportioned relative to the impedanceoi said secondary winding with a small current flowing therein at saidfrequency as to provide an oscillatory condition in the nature of seriesresonance, the impedance 0! said secondary winding varying upon anincreasing flow of current so as tomore closely approach the impedanceof said condenser until a stable series resonant condition is reachedwith amaximum current flow corresponding to optimum operation of saidtube and to the maxi, mum flux density oi the secondary section of saidcore? thereby limiting said current flow regardless of said negativeimpedance characteristic of said tube. p

JOSEPH G. SOLA.

